Our aim is to continue studies of the mechanics of the heart. We have been interested in the dynamics of contraction, the long-term goal being to relate properties at the sarcomere and molecular level to contraction in the myocardium. The present experiments, in particular, are designed to explore the implications of stepwise shortening. We have found that shortening occurs in discrete steps, synchronized over a large region of space and punctuated by pauses. This is unexpected according to current ideas about the contractile process; yet we have now confirmed it by four independent methods. Among the questions we wish to answer are: (1) Do steps occur in single myofibrillar sarcomers? (2) Is myosin critical for the presence of stepwise shortening? (3) Is step size quantized? (4) What is the mechanism of synchrony? (5) Does the pause precede the step, or vice-versa? (6) What is the role of activation? These questions will be answered using state of the art sensors to measure sarcomere and segment dynamics.